Momentum transfer process, heat transfer process and mass transfer process are called "three-transfer theory"

There is relative motion between the fluid flowing by momentum transfer and the adjacent fluid layer or pipe wall. Momentum of high-speed and high-momentum fluid will be transferred to the boundary layer of adjacent low-speed fluid layer or wall, which is called momentum transfer. Heat transfer is a complex phenomenon, which is usually divided into three basic ways, namely heat conduction, heat convection and heat radiation. The heat transfer phenomenon in production and life is often the combination of different primary and secondary of these three basic ways. Due to the difference of chemical potential, the substance moves from the part with high chemical potential to the part with low chemical potential in the medium, which is listed as three transfer processes together with momentum transfer and heat transfer. Mass transfer can be carried out in one phase or in interphase. The difference of chemical potential can be caused by concentration, temperature, pressure and applied electric field. Mass transfer is a common phenomenon.